This invention relates to motor fuel compositions for a spark ignited internal combustion engine. More specifically, this invention relates to a motor fuel composition for use in an internal combustion engine which results in reduced hydrocarbon emissions in the exhaust gas. In particular, this invention relates to a liquid hydrocarbon fuel of the gasoline boiling range containing, as an antiknock, a cyclopentadienyl manganese compound and, as an exhaust emission reducing additive, a polyester of a polymerized carboxylic acid.
Fuels used in today's automotive engines cause deposits to be formed during combustion. Formation of these deposits in the combustion chambers of the engine can result in increased amounts of unburned or partially oxidized hydorcarbons emitted with the engine exhaust gas. Such unburned hydrocarbons tend to react with other atmospheric substituents to substantially contribute to air pollution. Cyclopentadienyl manganese compounds have proven to be excellent antiknocks in gasolines used to operate internal combustion engines. They have been especially beneficial in solving some of the problems present when low-lead or lead-free gasolines are used with internal combustion engines. Use of such compounds as antiknocks is described in U.S. Pat. Nos. 2,818,417, 2,839,552 and and 3,127,351, all incorporated herein by reference. It is believed, however, by some researchers in the field, that the presence of certain of these organomanganese antiknocks in some of today's low-lead or lead-free gasoline motor fuels tend, in some manner, not altogether fully understood, to promote or increase the amount of unburned and/or partially oxidized hydrocarbons emitted from an engine which is operated on such a fuel. Thus, a need exists for a method to reduce the amount of unburned or partially oxidized hydrocarbons introduced into the atmosphere from the exhaust gas of an internal combustion engine operating on a lead-free or substantially lead-free gasoline containing, as an antiknock, a cyclopentadienyl manganese antiknock compound. In the past, there have been efforts to reduce the amount of exhaust hydrocarbon emissions produced by the consumption of unleaded fuel in automobile engines. For example, U.S. Pat. No. 4,175,927 discloses the addition of a dimer acid and/or a trimer acid produced by the polymerization or condensation of an unsaturated aliphatic monocarboxylic acid having between 16 and 18 carbon atoms to gasoline containing a cyclopentadienyl manganese tricarbonyl antiknock to reduce hydrocarbon emissions in an engine operating on such a fuel. So far as is known, however, no effort has been made to reduce hydrocarbon emissions from an internal combustion engine operating on an unleaded gasoline containing a cyclopentadienyl manganese antiknock by incorporating into the gasoline esters of a polymerized carboxylic acid. U.S. Pat. No. 3,574,574 discloses the addition of fully esterified esters prepared from the dimer and trimer acids produced by the polymerization or condensation of an unsaturated aliphatic monocarboxylic acid having between 16 and 18 carbon atoms per molecule to gasoline containing a tetraalkyl lead compound. Reportedly, the presence of the ester additives in leaded gasoline reduces or eliminates the accumulation of harmful deposits composed of the by-products of fuel combustion and lubricating oil deterioration which forms on the intake valves and around the port areas of the engine operating on the leaded fuel. U.S. Pat. Nos. 2,849,399 and 4,167,486 disclose polymerized carboxylic acid esters as lubricity agents. U.S. Pat. No. 2,673,184 discloses a lubricating grease composition which comprises alcohol esters of dilinoleic acid thickened with a minor amount of lithium.